Integrated Geophysical Methods for Imaging The Subsurface of a Building Site

2017

English

Integrated geophysical investigation was carried out at a building site between the KNUST Finance Office and the University Hall to assess the subsurface structure and delineate any unknown fissures, joints and fractures that might pose any danger to the development of the site as well as map the various structural features present within the subsurface. Three geophysical methods namely Continuous Vertical Electrical Sounding (CVES), Ground penetrating Radar (GPR) and the Seismic Refraction were employed on 7 profiles each of length 80m and at inter-profile separation of 4m. The geophysical model of the site suggested a top layer material of thickness 3m with resistivity values above 700Ωm overlying a moderately–slightly weathered material with slightly lower resistivity. The seismic refraction survey suggested a 2 layer model with top layer velocities in the range 480-630m/s and 2000-2500m/s for the refractor, intercepted at the depth between 7-9m. The top 3m in depth which marked the hard surface on the CVES correlated well with that on the GPR radiograms. No faults, fractures, cavities or any structural feature of serious implications on building foundations could be identified. The GPR detected groundwater at the depth of 16m possibly located within the moderately –slightly weathered formation. Sections on the CVES close to the surface recording low resistivity were attributed to seepage from conduit pipes or zones with high moisture content. Despite these advantages of integrated geophysical methods in site investigation, anomalous areas in the survey area need to be further investigated by direct boring and testing which in this project could be limited to few holes thus reducing the budget and further emphasizing the need to use geophysics as a practical tool subsurface imaging and planning of building development projects.

Nyako, S. O.; Akyeampong, A. A.; Ofosu, B.; Opuni, K. O.; Mensah, F. A.